Mercer County has embraced modern roundabouts as a tool to keep traffic moving, reduce crashes, and improve safety for everyone. Modern roundabouts are NOT traffic circles. A modern roundabout operates by different rules than a classic traffic circle and is designed differently. Mercer County is one of many jurisdictions throughout the State of New Jersey and throughout the Country that has embraced modern roundabouts as alternatives to traffic signals. As our traffic signals age and need replacement or wherever an intersection needs to be improved for safety or operational purposes, Mercer County will evaluate if a traffic signal, stop control, or modern roundabout is the best alternative for each respective location.

Safety Benefits of Modern Roundabouts

 There are several benefits to modern roundabouts that make them better alternatives to a signalized intersection. Due to the physical design of modern roundabouts, vehicles are required to approach at lower speeds and at a prescribed angle. Both of these factors mean that the most dangerous types of crashes, head-on and right-angle collisions (t-bone crashes), are eliminated. In a modern roundabout, traffic is forced to travel in the same direction at a lower speed and the number of conflict points is reduced to eight (8) potential conflict points vs. 32 at a traditional intersection. With fewer and less severe conflict points, pedestrians also benefit from shorter, more manageable crossings and slower vehicle approach speeds, further improving safety.

The Federal Highway Administration (FHWA) reports that modern roundabouts reduce fatal and injury crashes by 82% when replacing a two-way stop sign controlled intersection and 78% when replacing a signalized intersection. (FHWA, 2019[MC1] )

Operational Efficiency Benefits

Roundabouts can also improve traffic flow and reduce vehicle delays compared to traffic signals, particularly under moderate traffic volumes. Because vehicles yield rather than stop and wait for a green light, roundabouts minimize unnecessary idling and keep vehicles moving when gaps are available. This efficiency extends to multiple approaches, as the circulating flow allows balanced, continuous movement from all directions without the “dead time” inherent in traffic signal cycles.

Environmental Benefits
By reducing idling, stop-and-go driving, and unnecessary acceleration, roundabouts can lower vehicle emissions and fuel consumption. The smoother flow not only benefits drivers economically but also contributes to improved local air quality. Over time, especially in areas with frequent congestion, these environmental gains can add up, aligning roundabout design with broader sustainability and climate goals.

A study by the Insurance Institute for Highway Safety (IIHS) estimated that the conversion of 10 percent of the signalized intersections in the United States to roundabouts would have reduced vehicle delays by more than 981 million hours and fuel consumption by more than 654 million gallons in 2018.

Cost Savings and Longevity Benefits

While the initial construction cost of a roundabout can be higher than installing traffic signals, roundabouts often have lower long-term operating and maintenance expenses. They require no electrical power for signal operation and avoid costs associated with regular signal maintenance, bulb replacement, and software updates. During major weather events or emergencies where power goes out, a modern roundabout is still able to safely operate and move traffic. There is no need to station a person to manage and direct traffic unlike at major signalized intersections. Not only does this keep police and personnel out of harm’s way but also frees them up for other more important emergency functions when they do not have to manage traffic.

Additionally, the safety benefits translate into substantial societal cost savings by reducing crash-related medical expenses, property damage, and emergency response needs. When factoring in lifespan, operational savings, and safety-related cost avoidance, roundabouts often offer a higher return on investment than traditional intersection controls.

Emergency Response Benefits

Modern roundabouts—when designed with truck aprons and clear signage—do not harm emergency service response times and may even improve safety and access. Studies in cities across the United States found no statistically significant difference in fire and EMS response times before and after implementing roundabouts or similar traffic-calming designs.

Drivers

• Slow Down on approach and look for signage and lane markings
• Always yield to traffic already in the roundabout
• Always yield to pedestrians in crosswalks
• Only enter when a safe gap appears
• Stay in your lane — do not change lanes once inside
• Use turn signal right before your exit
• Watch for pedestrians/bicyclists in crosswalks. Yield to bikes and peds.

Cyclists

• Option 1: Ride as a vehicle (take the lane)
• Option 2: Use sidewalk and crosswalks as a pedestrian
• Always signal and make eye contact with drivers
• If crossing as pedestrian, press RRFB push buttons before crossing to signal to drivers

Pedestrians

• Use designated crosswalks and press RRFB push buttons before crossing to signal to drivers
• Wait for a gap in traffic or for drivers to yield
• Cross one lane at a time to the splitter island

Additional Resources:

Roundabouts

Myths and Facts about Roundabouts